| China is plenty in boron resources and most boron resources exist in the forms of ascharite and ludwigite ore in Liaoning Province. Among these, ascharite ore is the main raw material of production of boric acid and borax. Nevertheless, the storage as well as the average grade of ascharite resources is deceasing due to the continuous mining in recent years. Thus, the comprehensive usage of boron resources is the key to its shortage. The selective reduction of ludwigite in the blast furnace will result in boric pigiron and boron-rich slag. The grade of the boron-rich slag, which is a kind of artificial mineral, could be the relatively high to12%-17%. At the same time, boron-rich slag could replace the ascharite ore to be the source of magnesium and boron because its similarity to the roasting ascharite.Based on the potential-pH diagram of B-H2O system, the experiment analyzed the stable existing form of boron ions in liquid phase and combined alkaline leaching reaction theory to investigate the factors which included the reaction time, reaction temperature, liquid-solid ratio, quantity of alkali and mixing speed contributing to the performance of leaching boron-rich slag. The result defined the best technology conditions for the boron-rich slag alkaline leaching method under ordinary pressure. The best technology conditions for the14.01%grade boron-rich slag alkaline leaching under ordinary pressure method were95℃reaction temperature,5h reaction time,3:1solid-liquid ratio,1.2:1quantity of alkaline and200r/min mixing speed. Under such conditions, the leaching rate of B2O3was49.55%. At the same time, it also investigated the leaching performance of boron-rich slag at lower grade. The result showed that the best technology conditions for the11.91%grade boron-rich slag alkaline leaching under ordinary pressure were100℃reaction temperature,6h reaction time,3:1solid-liquid ratio,1.4:1quantity of alkaline and200r/min mixing speed. Under such conditions, the leaching rate of B2O3was51.43%. The different boron-rich slag alkaline leaching rates of different grades under ordinary pressure revealed that the slight increasing of reaction time, reaction temperature, quantity of alkaline and the stability of the leaching rate of B2O3(around50%) as the decreasing of mineral grade. In conclusion, the alkaline leaching method under ordinary pressure had minimal influence on the leaching rate of B2O3of boron-rich slag of12%-14%grade.During the process of alkaline leaching, the Ca2+and Si4+impurity were also leached and flooded into the leachate at liquid phase with boron ions. The experiment studied the technology of getting rid of impurities Ca2+and Si4+from leachate, and the best experimental condition for it: first adding3g NaHCO3into the leachate, at this moment, the Ca2+in the boron leaching liquid was almost removed. Also, the H2BO3-had turned into B4O72-completely. Then, the Si4+removal rate was up to99%when regulating the pH value to9.0. This could reach the purpose of "one-step method" to remove impurities, and provided the theoretical and technical support to produce boron of high purity. During the crystallinzation test, the experiment analyzed the factors such as the temperature of crystallization, the cooling method and the time of crystallization, which could influence the rate of borax crystallization. The experiment also defined the parameters of optimal condition for borax crystallization:The temperature of crystallization stayed at5℃, the time of crystallization was12h, and combined with the two-phase cooling method, all these conditions could make the crystallization rate of borax up to73%. The crystal in this experiment could be uniform in form and good in crystal growth, which meant the purity of it could reach97%or above, which could meet the requirement of the Grade Ⅱ national standards for borax quality (GB/T537-2009).The alkaline leaching of producing borax under ordinary pressure method has advantages such as short reaction time, no high-pressure conditions, no feeding air process, less equipment, safe and simple to operate, etc. This paper adopted the alkaline leaching under ordinary pressure method to leach boron-rich slag, which provided the theoretical evidence and technical support to boron-rich slag comprehention. |
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